1. Field of the Invention
The present invention relates to a power tool, and more particularly, to a technique of reducing vibration in a power tool, such as a hammer and a hammer drill, which linearly drives a hammer bit at a predetermined cycle.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 52-109673 discloses a hammer with a vibration reducing device. According to the known art, a vibration-isolating chamber is integrally formed within the body housing and a dynamic vibration reducer is housed within the vibration-isolating chamber. The dynamic vibration reducer serves to reduce vibration in relation to the amount of vibration inputted into the dynamic vibration reducer. Especially within the hammer, strong vibration may be developed in the axial direction of the hammer bit when the hammer is operated.
In the above-explained dynamic vibration reducer, the weight is disposed under the action of the biasing force of an elastic element. The dynamic vibration reducer performs a vibration reducing function by the weight being driven according to the amount of vibration that is inputted to the dynamic vibration reducer. Specifically, the dynamic vibration reducer has a passive property that the amount of vibration reduction by the dynamic vibration reducer depends on the amount of imputed vibration. On the other hand, in the actual operation using the power tool, the user who holds the power tool may possibly press the power tool strongly against the work piece in order to perform the work onto the work piece. In such a case, although vibration reduction is highly required, the vibration amount inputted to the dynamic vibration reducer may be reduced because the user strongly presses the power tool against the work piece. Thus, almost of the vibration is transmitted to the body of the user of the power tool. Therefore, dynamic vibration reducer that can alleviate the vibration without respect to the amount of vibration imputed to the dynamic vibration reducer is needed.